JP2012197507A - High-strength steel pipe having excellent toughness at low temperature and sulfide stress corrosion cracking resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-strength steel pipe with excellent toughness at low temperature and sulfide stress corrosion cracking resistance.SOLUTION: The high-strength steel pipe has a steel composition controlled in a specific range and has a microstructure comprising low bainite of about 60 vol.% or more and about 40 vol.% or less without substantial formation of ferrite, high bainite, or granular bainite. The microstructure is obtained by quenching the pipe and, after quenching, tempering the pipe.

Description

  The present invention relates generally to the manufacture of metals and, in particular embodiments, to a method of manufacturing a tubular metal rod having high toughness at low temperatures while simultaneously having sulfide stress corrosion crack resistance. Specific embodiments include all types of vertical pipes (suspended, mixed, top tensioned, retrofitted, drilled, etc.), including pipes suitable for bending, piping and use in the oil and gas industry Relating to seamless steel pipes for flow conduits.

  A central element in deep and ultra deep sea production is the circulation of fluid from the sea floor to the surface system. Vertical pipes, i.e., pipes that connect drilling or production platforms to oil wells, can be a significant distance (today about 10,000 feet (3.3 km) or about 2 miles) against the stress of many ocean currents. Over 3.2 km).

  The cost of a vertical pipe system is extremely sensitive to water depth. Sensitivity to operating conditions and environmental loads (ie waves and ocean currents), different vertical tube types-top tension vertical tube (TTR) and steel suspended tube (SCR), mixed vertical tube (HR), refurbishment Although different for molds (WOR) and drilled vertical pipes (DR), reducing the weight of vertical pipes provides important advantages. For example, it is anticipated that by reducing the weight of the conduit, significant impact reduction on the price of the tube and the traction system used to support the vertical tube can be achieved. For at least these reasons, high strength steel with a yield stress of 70 ksi (485 MPa) or more is a candidate for the development of lighter vertical pipes in the offshore industry sector.

However, steels with a specific minimum yield strength (SMYS) greater than 70 ksi can undergo sulfide stress corrosion (SSC) induced failure as a result of hydrogen embrittlement under stress. Thus, NACE conditions for acidic use materials (eg NACE MR0175 / ISO15156-1 “Oil and Natural Gas Industry—Materials for Use in H ₂ S-Containing Environments in Oil and Gas Production—Part 1: Crack Resistant Materials And pass the SSC test (eg NACE Standard TM0177 “Metal Lab Test for Resistance to Sulfide Stress Cracking and Stress Corrosion Cracking in H ₂ S Environments”) It is difficult.

  Major seamless line tube manufacturers can produce high strength materials with a minimum yield strength of 70 ksi or higher, but these high grades are resistant to SSC and hydrogen induced cracking (HIC) ( This latter is often not appropriate according to the NACE standard TM0284, "Evaluation of resistance to hydrogen-induced cracks, pipe and pressure vessel steel". Currently, only upgrades to X70 are qualified for acidic use according to ISO 3183.

  Furthermore, increased strength can lead to more fragile dynamics at lower temperatures. In general, materials are qualified at the so-called “design temperature”, which is typically about 20 ° C. below the lowest expected use temperature and / or ambient temperature. The minimum ambient temperature on the Norwegian continental shelf is about -20 ° C. In the Atlantic region, the lowest ambient temperature well below -40 ° C is expected. As a result, a minimum design temperature of up to about −60 ° C. is desired.

However, line tube steels with a yield stress of about 70 ksi or more are today qualified for design temperatures only up to about −40 ° C. This limitation may constrain cost-effective oil and gas searches in the Atlantic and similar regions.

  Therefore, new, high strength steel pipes with improved toughness at temperatures below about −60 ° C. are desired.

Summary Aspects of the present invention relate to steel pipes or tubes and methods of making the same. In some embodiments, wall thickness (WT) between 8 and 35 mm with minimum yield strength of 70 ksi, 80 ksi and 90 ksi, respectively, with excellent toughness and corrosion resistance at low temperatures (acid use, H ₂ S environment). Seamless quenched and tempered steel pipes are provided for vertical and line pipes having Seamless tubes are also suitable for producing identical grade bends by heat induced bending and off-line quenching and tempering processes. In one embodiment, the steel pipe has an outer diameter (OD) between 6 ″ (152 mm) and 28 ″ (711 mm) and a wall thickness (WT) of 8 to 35 mm.

  In one embodiment, the composition of the seamless low alloy steel pipe is with the balance of iron and inevitable impurities, the following (weight): 0.05% -0.16% C, 0.20% -0. 90% Mn, 0.10% -0.50% Si, 1.20% -2.60% Cr, 0.05% -0.50% Ni, 0.80% -1.20% Mo, up to 0.03% Nb, up to 0.02% Ti, 0.005% -0.12% V, 0.008% -0.040% Al, 0.0030-0.012 % N, up to 0.3% Cu, up to 0.01% S, up to 0.02% P, 0.001-0.005% Ca, up to 0.0020% B, up to 0. 020% As, max 0.0050% Sb, max 0.020% Sn, max 0.030% Zr, max 0.030% Ta, max .0050% of Bi, up to 0.0030% or the O, up to 0.00030% of H, the more.

Steel pipes can be manufactured in different grades. In one embodiment, the 70 ksi grade is provided with the following properties:
Yield strength, YS: minimum 485 MPa (70 ksi) and maximum 635 MPa (92 ksi),
-Ultimate tensile strength, UTS: minimum 570 MPa (83 ksi) and maximum 760 MPa (110 ksi),
・ Elongation rate, 20% or more,
-YS / UTS ratio is 0.93 or less.

In other embodiments, the 80 ksi grade is provided with the following properties:
Yield strength, YS: minimum 555 MPa (80 ksi) and maximum 705 MPa (102 ksi),
-Ultimate tensile strength, UTS: minimum 625 MPa (90 ksi) and maximum 825 MPa (120 ksi),
・ Elongation rate, 20% or more,
-YS / UTS ratio is 0.93 or less.

In other embodiments, the 90 ksi grade is provided with the following properties:
Yield strength, YS: minimum 625 MPa (90 ksi) and maximum 775 MPa (112 ksi),
-Ultimate tensile strength, UTS: minimum 695 MPa (100 ksi) and maximum 915 MPa (133 ksi),
・ Elongation rate, 18% or more,
-YS / UTS ratio is 0.95 or less.

  The steel pipe has a minimum impact energy of 250 J / 200 J (average / individual) and a minimum of 80% for both longitudinal and lateral Charpy V-notch (CVN) tests performed at about -70 ° C. according to standard ISO 148-1. It can have an average shear area. In one embodiment, an 80 ksi grade tube can have a hardness of up to 248 HV10. In other embodiments, 90 ksi grade tubes can have a hardness of up to 270 HV10.

Steel pipes manufactured in accordance with aspects of the present invention can exhibit resistance to both hydrogen induced cracking (HIC) and sulfide stress corrosion (SSC) cracking. In one embodiment, the HIC test performed according to NACE Standard TM0284-2003, paragraph 21215, using NACE solution A and a test duration of 96 hours, gives the following HIC parameters (average of 3 of 3 specimens):
-Crack length ratio CLR < 5%,
・ Crack thickness ratio, CTR < 1%,
• Crack susceptibility ratio, CSR < 0.2%.

  In other embodiments, SSC tests performed according to NACE TM0177 using test solution A and test period 720 hours did not break in 70% and 80ksi grades 90% SMYS and failed in 90ksi grade 72% SMYS Not give.

  Steel tubes made according to certain embodiments of the present invention have a microstructure that does not exhibit any of ferrite, upper bainite, and granular bainite. They are tempered martensite with a volume percentage (measured according to ASTM E562-08) greater than 60%, preferably greater than 90%, most preferably greater than 95% and less than 40%, preferably less than 10% Most preferably, it may consist of tempered lower bainite containing a volume percentage of less than 5%. Martensite and bainite were reheated at a temperature of 900 ° C. to 1060 ° C. during a soaking time of 300 seconds to 3600 seconds, and after quenching at a cooling rate of more than 20 ° C./second, respectively less than 450 ° C. and 540 ° C. It can be formed at a temperature of less than 0C. The average prior austenite particle size, as measured by ASTM E112 standard, is greater than 15 μm or 20 μm (linear intercept) and less than 100 μm.

  In a further aspect, the steel tube packet size after tempering can have a packet size less than 6 μm (ie, the average size of the regions separated by high angle boundaries). In a further aspect, the packet size can be less than about 4 μm. In other aspects, the packet size can be less than about 3 μm. Packet size is the average in images taken by a scanning electron microscope (SEM) using electron backscatter diffraction (EBSD) signals with high angle boundaries that are considered to be boundaries with> 45 ° misorientation. It can be measured as a linear intercept.

In a further embodiment, the steel pipe after tempering can show the presence of fine and coarse precipitates. The fine precipitate can be of the type MX, M ₂ X, where M is V, Mo, Nb or Cr and X is C or N. The average particle size of the fine precipitate can be less than about 40 nm. The coarse precipitate can be of type M ₃ C, M ₆ C, M ₂₃ C ₆ . The average particle size of the coarse precipitate can be in the range between about 80 nm and about 400 nm. The precipitate can be examined by transmission electron microscopy (TEM) using an extraction replica method.

In one embodiment, a steel pipe is provided. The steel pipe is about 0.05 wt% to about 0.16 wt% carbon;
About 0.20 wt% to about 0.90 wt% manganese;
From about 0.10% to about 0.50% silicon by weight;
From about 1.20% to about 2.60% by weight chromium;
About 0.05% to about 0.50% nickel by weight;
From about 0.80% to about 1.20% by weight molybdenum;
From about 0.005% to about 0.12% by weight of vanadium;
About 0.008% to about 0.04% aluminum by weight;
From about 0.0030% to about 0.0120% by weight of nitrogen; and from about 0.0010% to about 0.005% by weight of calcium:
A steel composition comprising

  The wall thickness of the steel pipe can be about 8 mm or more and less than about 35 mm. The steel pipe can be processed to have a yield strength of greater than about 70 ksi, the microstructure of the steel pipe comprising about 60% or more volume percent martensite and about 40% or less volume percent low bainite. be able to.

In another aspect, a method for manufacturing a steel pipe is provided. The method comprises providing a steel (eg, a low alloy steel) having a steel composition. The method further comprises forming the steel into a tube having a wall thickness of about 8 mm or more and less than about 35 mm. The method further comprises heating the formed steel tube in an initial heating operation to a temperature in the range between about 900 ° C and about 1060 ° C. The method also includes the step of quenching the formed steel pipe at a cooling rate of about 20 ° C./second or more, wherein the microstructure of the quenched steel has about 60% or more martensite and about Less than 40% low bainite and having an average plier austenite particle size as measured by ASTM E112 greater than about 15 μm. The method further comprises the step of tempering the quenched steel pipe at a temperature in the range between about 680 ° C. and about 760 ° C., where the tempered steel pipe has a yield strength of greater than about 70 ksi and about It has an average Charpy V-notch energy of about 150 J / cm ² or greater at -70 ° C. In other embodiments, the average Charpy V-notch energy of the steel pipe is about 250 J / cm ² or more at about −70 ° C.

In one embodiment, an 80 ksi grade seamless steel pipe is provided. The tube
0.10% to 0.13% by weight of carbon;
0.40% to 0.55% manganese by weight;
0.20 wt% to 0.35 wt% silicon;
1.9 wt% to 2.3 wt% chromium;
0.9 wt% to 1.1 wt% molybdenum;
0.001 wt% to 0.005 wt% calcium;
0.05 wt% to 0.07 wt% vanadium and 0.010 wt% to 0.020 wt% aluminum;
A steel composition comprising The thickness of the steel pipe is about 8 mm or more and about 35 mm or less. The steel tube is hot-rolled, then cooled to room temperature, heated to a temperature of about 900 ° C. or higher, quenched at a cooling rate of 40 ° C./second or higher, and tempered at a temperature between about 680 ° C. and about 760 ° C. To form a microstructure having a prior austenite particle size of about 20 μm to about 60 μm, a packet size of about 3 μm to about 6 μm, and a martensite of about 90% by volume or more and a low bainite of about 10% by volume or less. Can do. The steel pipe has a yield strength (YS) between about 80 ksi and about 102 ksi, an ultimate tensile strength (UTS) between about 90 ksi and about 120 ksi, an elongation of about 20% or more and a YS / UTS ratio of 0.93 or less. be able to.

In another aspect, a 90 ksi grade seamless steel pipe can be provided. The tube
0.10% to 0.13% by weight of carbon;
0.40% to 0.55% manganese by weight;
0.20 wt% to 0.35 wt% silicon;
1.9 wt% to 2.3 wt% chromium;
0.9 wt% to 1.1 wt% molybdenum;
0.001 wt% to 0.005 wt% calcium;
0.05 wt% to 0.07 wt% vanadium; and 0.010 wt% to 0.020 wt% aluminum;
A steel composition comprising The wall thickness of the steel pipe can be about 8 mm or more and about 35 mm or less. The steel tube is hot rolled, followed by cooling to room temperature, heating to a temperature of about 900 ° C. or higher, quenching at a cooling rate of about 20 ° C./second or more, and baking at a temperature between about 680 ° C. and about 760 ° C. Processed by reversion to form a microstructure having a prior austenite particle size of about 20 μm to about 60 μm, a packet size of about 2 μm to about 6 μm, and a martensite of about 95% by volume or more and a low bainite of about 5% by volume or less. be able to. The steel pipe has a yield strength (YS) between about 90 ksi and about 112 ksi, an ultimate tensile strength (UTS) between 100 ksi and 133 ksi, an elongation of about 18% or more and a YS / UTS ratio of about 0.95 or less. Can do.

In a further aspect, a 70 ksi grade seamless steel pipe can be provided. The tube
0.10% to 0.13% by weight of carbon;
0.40% to 0.55% manganese by weight;
0.20 wt% to 0.35 wt% silicon;
2.0 wt% to 2.5 wt% chromium;
0.9 wt% to 1.1 wt% molybdenum; and 0.001 wt% to 0.005 wt% calcium;
A steel composition comprising The wall thickness of the steel pipe can be about 8 mm or more and about 35 mm or less. The steel tube is hot rolled, followed by cooling to room temperature, heating to a temperature of about 900 ° C. or higher, quenching at a cooling rate of about 20 ° C./second or more, and baking at a temperature between about 680 ° C. and about 760 ° C. Processed by reversion to form a microstructure with a prior austenite particle size of about 20 μm to about 100 μm, a packet size of about 4 μm to about 6 μm, and a martensite of about 60% or more by volume and a low bainite of about 40% or less by volume. be able to. The steel pipe has a yield strength (YS) between about 70 ksi and about 92 ksi, an ultimate tensile strength (UTS) between about 83 ksi and about 110 ksi, an elongation of about 18% or more, and a YS / UTS ratio of about 0.93 or less. Can have.

Other features and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings.
FIG. 1 is a scheme flow diagram showing one embodiment of a method for processing a steel pipe. FIG. 2 is an embodiment of a continuous cooling transformation (CCT) diagram of one embodiment of the steel of the present disclosure. FIG. 3 is an optical micrograph of an as-quenched tube formed in accordance with the disclosed embodiment using a retention time of about 600 seconds. The tube is etched to represent the boundaries of the prior austenite particles. FIGS. 4A and 4B are optical micrographs of as-quenched and tempered tubes formed according to the disclosed embodiment using a retention time of about 2400 seconds. The tube is etched to represent the boundaries of the prior austenite particles. (4A) 200 times magnification, (4B) 1000 times magnification. FIG. 5 is a photomicrograph taken by a scanning electron microscope (SEM) using an electron backscatter diffraction (EBSD) signal, representing the boundary with both low and high in the approximately central wall portion of the tube of FIG. is there. FIG. 6 is a plot representing the distribution of the intercept of the boundary having an angular misalignment greater than about 45 ° for steel formed according to the disclosed embodiments. FIG. 7 is an optical micrograph of the vicinity of the central wall of the as-quenched tube of the comparative example of Example 3.

DETAILED DESCRIPTION Embodiments of the present disclosure provide a steel composition, a tubular rod (eg, a tube) formed using the steel composition, and a method for making each. Tubular rods can be used, for example, as line and vertical tubes for use in the oil and gas industry. In certain embodiments, the tubular rod can have a wall thickness of about 8 mm or more and less than about 35 mm and a martensite and low bainite microstructure free of substantial ferrites, high bainite or granular bainite. Tubular bars so formed can have minimum yield strengths of about 70 ksi, 80 ksi, and about 90 ksi. In a further aspect, the tubular rod can have good toughness at low temperatures and resistance to sulfide stress corrosion cracking (SSC) and hydrogen induced cracking (HIC), thereby enabling the use of the tubular rod in an acidic use environment To. However, it should be understood that the tubular rod comprises an example of a product that can be formed from the embodiments of the present disclosure and should in no way be considered as limiting the applicability of the disclosed embodiments. Can do.

  The term “stick” as used herein is a broad term, including the meaning found in its normal dictionary, and is also straight or has a bend or curve and is determined in advance. Represents a generally hollow, elongated member that can be formed into a shaped shape, as well as any additional molding material necessary to secure the formed tubular rod to its intended site. Other shapes and cross-sections are envisioned as well, but the rod can be tubular with a substantially circular outer surface and an inner surface. The term “tubular” as used herein refers to any elongated hollow shape that need not be circular or cylindrical.

  As used herein, the terms “roughly”, “about” and “substantially” refer to amounts that are close to the stated amount and that still achieve the desired function or achieve the desired result. To express. For example, the terms “approximately”, “about” and “substantially” include less than 10%, less than 5%, less than 1%, less than 0.1%, and less than 0.01% of the stated amount. A certain amount can be expressed.

  The term “room temperature” as used herein has its ordinary meaning known to those skilled in the art and includes temperatures in the range of about 16 ° C. (60 ° F.) to about 32 ° C. (90 ° F.). Can do.

  Embodiments of the present disclosure comprise a low alloy carbon steel pipe and a process. As will be described in more detail below, the combination of steel composition and heat treatment can result in minimum yield strength, toughness, hardness and corrosion in high wall thickness tubes (eg, WT greater than about 8 mm and less than about 35 mm). A final microstructure can be achieved that provides specific mechanical properties of interest, including one or more of the resistors.

The steel composition of the present disclosure includes not only carbon (C) but also manganese (Mn), silicon (Si), chromium (Cr), nickel (Ni), molybdenum (Mo), vanadium (V), aluminum (Al ), Nitrogen (N) and calcium (Ca). Furthermore, optionally in the presence of one or more of the following elements: tungsten (W), niobium (Nb), titanium (Ti), boron (B), zirconium (Zr) and tantalum (Ta), and / Or may be added as well. The balance of the composition can comprise iron (Fe) and impurities. In certain embodiments, the concentration of impurities can be reduced to as low an amount as possible. Although the aspect of an impurity is not limited to them, copper (Cu), sulfur (S), phosphorus (P), arsenic (As), antimony (Sb), tin (Sn), bismuth (Bi), oxygen (O ) And hydrogen (H).

For example, the low alloy steel composition is as follows (% by weight unless otherwise noted):
Carbon in the range between about 0.05% and about 0.16%;
Manganese in a range between about 0.20% and about 0.90%;
Silicon in a range between about 0.10% and about 0.50%;
Chromium in a range between about 1.20% and about 2.60%;
Nickel in a range between about 0.050% and about 0.50%;
Molybdenum in a range between about 0.80% and about 1.20%;
Up to about 0.08% tungsten;
Less than or equal to about 0.030% niobium;
Up to about 0.020% titanium;
Vanadium within a range between about 0.005% and about 0.12%;
Aluminum in a range between about 0.008% to about 0.040%;
Nitrogen in the range between about 0.0030% and about 0.012%;
Up to about 0.3% copper;
Up to about 0.01% sulfur;
Up to about 0.02% phosphorus;
Calcium within a range of between about 0.001 to about 0.005%;
Up to about 0.0020% boron;
About 0.020% or less of arsenic;
About 0.005% or less of antimony;
Up to about 0.020% tin;
Up to 0.030% zirconium;
0.030% or less tantalum;
Less than about 0.0050% bismuth;
Less than about 0.0030% oxygen;
Up to about 0.00030% hydrogen; and a balance of the composition comprising iron and impurities:
Can comprise.

  The heat treatment operation can include quenching and tempering (Q + T) operations. The quenching operation can include a step of reheating the tube from about room temperature to a temperature at which the tube is austenitized after thermoforming and then rapidly quenching. For example, the tube can be heated to a temperature in the range of between about 900 ° C. and about 1060 ° C. and maintained at about the austenitizing temperature for a specified immersion time. The cooling rate during the quenching period is selected to achieve a specific cooling rate near the center of the tube wall. For example, the tube can be cooled to achieve a cooling rate of about 20 ° C./second or more in the middle of the wall. In other embodiments, the cooling rate can be about 40 ° C./second or more, as detailed below.

Quenching a tube having a WT greater than or equal to about 8 mm and less than about 35 mm and the composition described above has a capacity greater than about 60%, preferably greater than about 90%, and more preferably greater than about 95% in the tube. The formation of percent martensite can be enhanced. In certain embodiments, the remaining microstructure of the tube can comprise low bainite, substantially free of ferrite, high bainite or granular bainite. In other embodiments, the microstructure of the tube can consist essentially of 100% martensite.

After the quenching operation, the tube can be further tempered. Tempering can be carried out at a temperature in the range between about 680 ° C. and about 760 ° C., depending on the steel composition and the desired yield strength. The microstructure can further indicate the average plier austenite particle size measured according to ASTM E112, between about 15 μm and about 100 μm, in addition to martensite and low bainite. The microstructure can also exhibit an average packet size of about 6 μm or less, preferably about 4 μm or less, and most preferably about 3 μm or less. The microstructure further comprises a fine precipitate of MX, M ₂ X [where M = V, Mo, Nb, Cr and X = C or N] having an average particle size of about 40 nm or less, and between about 80 and about 400 nm. Coarse precipitates of type M ₃ C, M ₆ C and M ₂₃ C ₆ with an average particle size in the range of

In one embodiment, a steel pipe having a WT greater than or equal to about 8 mm and less than about 35 mm and the aforementioned composition and microstructure can have the following properties:
-Minimum yield strength (YS) = about 70 ksi (485 MPa)
Maximum yield strength = about 102 ksi (705 MPa)
・ Minimum ultimate tensile strength (UTS) = about 90 ksi (625 MPa)
・ Maximum ultimate tensile strength = about 120 ksi (825 MPa)
-Elongation rate at break = over about 20%-YS / UTS = about 0.93 or less.

In other embodiments, a steel pipe having a WT greater than or equal to about 8 mm and less than about 35 mm and the composition and microstructure described above can have the following properties:
-Minimum yield strength (YS) = about 80 ksi (550 MPa)
Maximum yield strength = about 102 ksi (705 MPa)
・ Minimum ultimate tensile strength (UTS) = about 90 ksi (625 MPa)
・ Maximum ultimate tensile strength = about 120 ksi (825 MPa)
-Elongation rate at break = over about 20%-YS / UTS = about 0.93 or less.

In other embodiments, a steel pipe having a WT greater than or equal to about 8 mm and less than about 35 mm can be formed with the following properties:
Minimum yield strength (YS) = about 90 ksi (625 MPa)
・ Maximum yield strength = about 112 ksi (775 MPa)
・ Minimum ultimate tensile strength (UTS) = about 100 ksi (695 MPa)
・ Maximum ultimate tensile strength = about 133 ksi (915 MPa)
・ Elongation at break = over about 18% ・ YS / UTS = about 0.95 or less.

In each of the above embodiments, the tube formed can further exhibit the following impact and hardness characteristics:
Minimum impact energy (average / individual, at about -70 ° C):
・ = About 250J / about 200J (for 70 ksi and 80 ksi grades)
・ = About 150J / about 100J (for 90ksi class)
Average shear area (CVN at about -70 ° C; ISO 148-1)
・ = About 80% minimum
・ Hardness ・ = Maximum about 248 HV ₁₀ (for 70 ksi and 80 ksi grades)
* = About 270 HV ₁₀ maximum (for 90 ksi grade).

In each of the foregoing embodiments, the formed tube can further exhibit the following resistance to sulfide stress corrosion (SSC) cracks and hydrogen induced cracks (HIC). The SSC test is performed according to NACE TM0177 using solution A with a test period of about 720 hours. The HIC test is performed according to NACE TM0284-2003, paragraph 21215, using NACE solution A and a test period of 96 hours:
HIC:
-Crack length ratio, CLR = 5% or less,
-Crack thickness ratio, CTR = 1% or less,
-Crack susceptibility ratio, CSR = 0.2% or less,
SSC:
Failure life at a specified minimum yield stress of 90%,
-= Over about 720 hours for 70 ksi and 80 ksi grades,
-Failure life at a specified minimum yield stress of 72%-= About 720 hours for 90 ksi grade.

  With reference to FIG. 1, a flow diagram depicting one aspect of a method 100 for manufacturing a tubular rod is shown. The method 100 includes a steelmaking operation 102, a thermoforming operation 104, an austenitizing 106A, a quenching 106B, a heat treatment operation 106 that may include a tempering 106C, and a finishing operation 110. It can be appreciated that the method 100 can include more or fewer operations, and the operations can be performed in a different order than that shown in FIG. 1, if desired.

  Operation 102 of the method 100 preferably comprises processing and drilling the steel, producing a solid metal billet that can be rolled to form a metal tubular rod. In a further embodiment, specific steel scrap, cast iron and sponge iron can be used to prepare the raw material for the steel composition. However, it can be appreciated that iron and / or other raw materials of steel can be used to prepare the steel composition.

  Primary steelmaking can be performed using an electric arc furnace to melt the steel, reduce phosphorus and other impurities, and achieve specific temperatures. Furthermore, tapping and deoxygenation and addition of alloy elements can be performed.

  One of the main objectives of the steelmaking process is the refining of iron by removing impurities. In particular, sulfur and phosphorus are detrimental to steel because they degrade the mechanical properties of the steel. In one embodiment, secondary steelmaking can be performed in a ladle furnace and trimming station after primary steelmaking to perform a specific refining process.

  During these operating periods, a very low sulfur content can be achieved in the steel, a calcium inclusion treatment is carried out and inclusion flotation is carried out. In one embodiment, inclusion flotation can be performed by bubbling an inert gas in a ladle furnace to float inclusions and impurities. This method produces a fluid slug that can absorb impurities and inclusions. In this way, it is possible to provide a high quality steel having a desired composition with a low inclusion content.

  Table 1 represents the embodiment of the steel composition in weight percent (weight,%) unless otherwise stated.

  Carbon (C) is an element whose addition to the steel composition can increase the strength of the steel inexpensively and refine the microstructure, thereby lowering the transformation temperature. In one embodiment, if the C content of the steel composition is less than about 0.05%, in some embodiments it may be difficult to obtain the desired strength for manufactured products, particularly tubular products. On the other hand, in other embodiments, if the steel composition has a C content greater than about 0.16%, in some embodiments, the toughness may be impaired and weldability may be reduced, Thus, if the joining is not performed by screw joining, any welding process can be made more difficult and expensive. Furthermore, the risk of quench cracking in steel with high hardenability increases with carbon content. Thus, in one embodiment, the C content of the steel composition is in the range between about 0.05% to about 0.16%, preferably in the range between about 0.07% to about 0.14%, and More preferably, it can be selected within a range between about 0.08% and about 0.12%.

Manganese (Mn) is an element whose addition to the steel composition can be effective in increasing the hardenability, strength and toughness of the steel. In one embodiment, if the Mn content of the steel composition is less than about 0.20%, in some embodiments it may be difficult to obtain the desired strength in the steel. However, in other embodiments, if the Mn content is greater than about 0.90%, in some embodiments, the band structure may become pronounced and toughness and HIC / SSC resistance may be reduced. Thus, in one embodiment, the Mn content of the steel composition is in the range between about 0.20% to about 0.90%, preferably in the range between about 0.30% to about 0.60%, and More preferably, it can be selected within a range between about 0.30% and about 0.50%.

  Silicon (Si) is an element whose addition to the steel composition can have a deoxygenating effect during the steel making process and can further increase the strength of the steel (eg, solid solution strengthening). In one embodiment, if the Si content of the steel composition is less than about 0.10%, the steel in some embodiments may have low deoxygenation during the steel making process and exhibit a high concentration of fine inclusions. is there. In other embodiments, both the toughness and formability of the steel may decrease in some embodiments when the Si content of the steel composition exceeds about 0.50%. Steel is treated at high temperatures (eg, temperatures above about 1000 ° C.) in an oxidizing atmosphere because surface oxide (scale) deposition is increased by iron olivine formation and the risk of surface defects increases. Occasionally, Si content in steel compositions above about 0.5% is also found to have a detrimental effect on surface quality. Accordingly, in one embodiment, the Si content of the steel composition is in the range between about 0.10% and about 0.50%, preferably in the range between about 0.10% and about 0.40%, and More preferably, it can be selected within a range between about 0.10% and about 0.25%.

  Chromium (Cr) is an element whose addition to the steel composition can increase the hardenability, lower the transformation temperature, and increase the tempering resistance of the steel. Thus, the addition of Cr to the steel composition may be desirable to achieve high strength and toughness levels. In one embodiment, it may be difficult to obtain the desired strength and toughness if the steel composition has a Cr content of less than about 1.2%. In other embodiments, when the Cr content of the steel composition is greater than about 2.6%, the price is excessive, and in some embodiments, the high deposition of coarse carbides at the grain boundaries reduces toughness. Might do. Furthermore, the weldability of the steel produced is reduced, which can make the welding process more difficult and expensive if the joining is not carried out by screw joining. Thus, in one embodiment, the Cr content of the steel composition is in the range between about 1.2% and about 2.6%, preferably in the range between about 1.8% and about 2.5%, More preferably, it can be selected within a range between about 2.1% and about 2.4%.

  Nickel (Ni) is an element whose addition to the steel composition can increase the strength and toughness of the steel. However, in one embodiment, if the Ni addition exceeds about 0.5%, an adverse effect on scale adhesion is observed and the risk of surface defect formation is high. Furthermore, in other embodiments, Ni content in the steel composition greater than about 1% is found to have a deleterious effect on sulfide stress corrosion cracking. Accordingly, in one embodiment, the Ni content of the steel composition is in the range between about 0.05% and about 0.5%, more preferably in the range between about 0.05% and about 0.2%. Can vary.

Molybdenum (Mo) is an element whose addition to the steel composition can improve hardenability and hardening by solid solutions and fine precipitates. Mo can help delay softening during tempering, thereby promoting the formation of very fine MC and M ₂ C precipitates. These particles are distributed substantially uniformly within the matrix, and further serve as beneficial hydrogen traps, thereby acting as crack nuclei, usually at the particle boundaries, the diffusion of atomic hydrogen towards dangerous traps Can be delayed. Mo further reduces phosphorus segregation to the grain boundaries, thereby improving resistance to intragranular failure, and high strength steels that suffer from hydrogen embrittlement exhibit an intragranular failure mode, thus reducing SSC resistance. Also has a beneficial effect. Therefore, by increasing the Mo content of the steel composition, the desired strength can be achieved at higher tempering temperatures that promote better toughness levels. In one embodiment, the Mo content of the steel composition can be about 0.80% or more in order to exert the effect. However, in other embodiments, if the Mo content in the steel composition exceeds about 1.2%, a saturation effect on hardenability is observed and weldability may be reduced. Because Mo iron alloys are expensive, in one embodiment, the Mo content of the steel composition is in the range between about 0.8% to about 1.2%, preferably about 0.9% to about 1. It can be selected within the range between 1% and more preferably within the range between about 0.95% and about 1.1%.

  Tungsten (W) is an element whose addition to the steel composition is optionally performed and can increase strength at room temperature and elevated temperature by forming tungsten carbide that forms a secondary cure. W is preferably added when it is necessary to use steel at high temperatures. The dynamics of W are similar to the dynamics of Mo with respect to hardenability, but the effect is about half that of Mo. Tungsten reduces the oxidation of the steel, and as a result, less scale is formed during the reheating process at high temperatures. However, because of its very high price, in one embodiment, the W content of the steel composition can be selected to be about 0.8% or less.

  Niobium (Nb) is optionally added to the steel composition and is provided to form carbides and nitrides, and further reduces the austenite grain size during hot rolling and reheating prior to quenching. An element that can be used for refining. However, due to the proper balance of other chemical elements such as Cr, Mo and C, a major martensitic structure is formed when low transformation temperatures are promoted and even in the case of coarse austenite particles, fine Since packets are formed, Nb is not necessary for the steel composition aspect of the present invention to refine austenite particles.

  Nb precipitates as carbonitride can increase the strength of the steel by dispersion hardening of the particles. These fine round particles are distributed substantially uniformly within the matrix and can further act as hydrogen traps, thereby leading to dangerous traps, usually at the particle boundaries, acting as crack nuclei. The diffusion of atomic hydrogen can be beneficially delayed. In one embodiment, when the Nb content of the steel composition exceeds about 0.030%, a coarse precipitate distribution may be formed that impairs toughness. Thus, in one embodiment, the steel composition may be selected such that the Nb content is about 0.030% or less, preferably about 0.015% or less, and more preferably about 0.01% or less. it can.

  Titanium (Ti) is an element whose addition to the steel composition is optionally performed and can be provided to refine the austenite grain size in the high temperature process, thereby forming nitrides and carbonitrides. However, embodiments of the steel composition of the present invention, except where it is used to protect boron remaining in solid solutions that improve hardenability, particularly in the case of tubes having a wall thickness greater than 25 mm. Is not necessary. For example, Ti binds nitrogen to avoid BN formation. Further, in certain embodiments, coarse TiN particles that impair toughness can be formed when Ti is present at a concentration greater than about 0.02%. Thus, in one embodiment, the Ti content of the steel composition can be about 0.02% or less, and more preferably about 0.01% or less when boron is less than about 0.0010%. .

Vanadium (V) is an element whose addition to the steel composition can increase strength by precipitation of carbonitride during tempering. These fine round particles are also distributed substantially uniformly within the matrix and can serve as beneficial hydrogen traps. In one embodiment, it may be difficult to obtain the desired strength when the V content is less than about 0.05%. However, in other embodiments, if the V content of the steel composition is higher than 0.12%, a large volume fraction of vanadium carbide particles is formed, which subsequently reduces toughness. Can do. Thus, in certain embodiments, the Nb content of the steel composition is about 0.12% or less, preferably in the range between about 0.05% to about 0.10%, and more preferably about 0.05%. ~ 0.07%
Can be selected to be within the range between.

  Aluminum (Al) is an element whose addition to the steel composition has a deoxygenating effect during the steel making process and can refine the steel particles. In one embodiment, when the Al content of the steel composition is greater than about 0.040%, coarse precipitates of AlN that impair toughness and / or oxides with high Al concentration that impair HIC and SSC resistance (eg, Non-metallic inclusions) can be formed. Thus, in one embodiment, the Al content of the steel composition may be selected to be about 0.04% or less, preferably about 0.03% or less, and more preferably about 0.025% or less. it can.

  Nitrogen (N), in one embodiment, is selected such that its content in the steel composition is preferably about 0.0030% or more to form carbonitrides of V, Nb, Mo and Ti. It is an element. However, in other embodiments, if the N content of the steel composition exceeds about 0.0120%, the toughness of the steel can be degraded. Accordingly, the N content of the steel composition is in the range between about 0.0030% to about 0.0120%, preferably in the range between about 0.0030% to about 0.0100%, and more preferably about It can be selected within the range between 0.0030% and about 0.0080%.

  Copper (Cu) is an impurity element that is not necessary for the embodiment of the steel composition. However, depending on the manufacturing process, the presence of Cu may be unavoidable. Therefore, the Cu content in the steel composition can be limited to be as low as possible. For example, in one embodiment, the Cu content of the steel composition can be about 0.3% or less, preferably about 0.20% or less, and more preferably about 0.15% or less.

  Sulfur (S) is an impurity element that can reduce both the toughness and workability of steel as well as the HIC / SSC resistance. Thus, in some embodiments, the S content of the steel composition can be kept as low as possible. For example, in one embodiment, the S content of the steel composition can be about 0.01% or less, preferably about 0.005% or less, and more preferably about 0.003% or less.

  Phosphorus (P) is an impurity element that can reduce the toughness and HIC / SSC resistance of high-strength steel. Thus, the P content of the steel composition can be kept as low as possible in some embodiments. For example, in one embodiment, the P content of the steel composition can be about 0.02% or less, preferably about 0.012% or less, and more preferably about 0.010% or less.

  Calcium (Ca) is an element whose addition to the steel composition can help control the shape of inclusions and promote HIC resistance by forming fine, substantially round sulfides. . In one embodiment, to provide these advantages, the Ca content of the steel composition is selected to be about 0.0010% or more when the sulfur content of the steel composition exceeds about 0.0020%. can do. However, in other embodiments, when the Ca content of the steel composition exceeds about 0.0050%, the effect of Ca addition is saturated and the non-metallic inclusions with high Ca concentration reduce the HIC and SSC resistance. The risk of forming lumps may increase. Thus, in certain embodiments, the minimum Ca content can be selected to be about 0.0010% or more, and most preferably about 0.0015% or more, while the maximum Ca content of the steel composition is about It can be selected to be 0.0050% or less, and more preferably about 0.0030% or less.

Boron (B) is an element whose addition to the steel composition is optionally performed and can be provided to improve the hardenability of the steel. B can be used to prevent ferrite formation. In one embodiment, the beneficial effect can be saturated with a boron content greater than about 0.0020%, but the lower limit of the B content of the steel composition to provide these beneficial effects is about 0.0005%. be able to. Thus, in certain embodiments, the B content of the steel composition is in the range between about 0 and 0.0020%, more preferably in the range between about 0.0005 and about 0.0012%, and most preferably. It can be in the range between about 0.0008% to about 0.0014%.

  Arsenic (As), tin (Sn), antimony (Sb), and bismuth (Bi) are impurity elements that are not necessary for the embodiment of the steel composition. However, the presence of these impurity elements may be unavoidable due to the steelmaking process. Accordingly, the As and Sn content in the steel composition can be selected to be about 0.020% or less, and more preferably about 0.015% or less. The Sb and Bi content can be selected to be about 0.0050% or less.

  Zirconium (Zr) and tantalum (Ta) are elements that act as strong carbide and nitride formers, similar to Nb and Ti. Since these elements are not necessary for the embodiment of the steel composition of the present invention to refine the austenite particles, they can be optionally added to the steel composition. The fine carbonitrides of Zr and Ta increase the strength of the steel by dispersion hardening of the particles and can further act as beneficial hydrogen traps, thereby delaying the diffusion of atomic hydrogen in the direction of dangerous traps. In one embodiment, if the Zr or Ta content is greater than or equal to about 0.030%, a coarse precipitate distribution can be formed that can impair the toughness of the steel. Zirconium also acts as a deoxygenating element in the steel and combines with sulfur, but Ca is preferred as an additive to the steel to enhance the non-metallic inclusions of the sphere. Accordingly, the Zr and Ta contents in the steel composition can be selected to be about 0.03% or less.

  The total oxygen (O) content of the steel composition is the sum of soluble oxygen and oxygen in the non-metallic inclusion (oxide). Too much oxygen content means a high volume fraction of non-metallic inclusions and a low resistance to HIC and SSC, as it is actually the oxygen content in the oxide in a fully deoxygenated steel. . Thus, in one embodiment, the oxygen content of the steel can be selected to be about 0.0030% or less, preferably about 0.0020% or less, and more preferably about 0.0015% or less.

  After production of a fluid slag having the above composition, the steel can be cast into a round solid billet having a substantially uniform diameter along the steel axis. For example, round billets having a diameter in the range between about 330 mm and about 420 mm can be produced in this way.

  The steel piece processed in this way can be formed into a tubular rod by the thermoforming step 104. In one embodiment, the clean steel, solid, cylindrical billet can be heated to a temperature of about 1200 ° C to 1340 ° C, preferably about 1280 ° C. For example, the billet can be reheated in a rotating heath furnace. The billet can be further subjected to a rolling mill. Within the rolling mill, the steel slab can be drilled using the Manesmann method in certain preferred embodiments, and hot rolling can be used to increase the outer diameter of the tube while substantially increasing the length. Substantially reduce wall thickness. In certain embodiments, the Manessemann method can be performed at a temperature in the range between about 1200 ° C and about 1280 ° C. The resulting hollow bar can be further hot-rolled in a holding mandrel continuous rolling mill at a temperature in the range between about 1000 ° C and about 1200 ° C. Accurate sizing can be performed by a sizing mill, and the seamless tube is air cooled to approximately room temperature in the cooling bed. In this manner, for example, a tube having an outer diameter (OD) in the range between about 6 inches (about 15 cm) and about 16 inches (about 40 cm) can be formed.

After rolling, in order to make the temperature more uniform, the tube can be heated in-line by an intermediate furnace without cooling at room temperature, and accurate sizing can be performed by a sizing mill. The seamless tube can then be air cooled to room temperature in the cooling bed. For tubes with a final OD greater than about 16 inches (about 40 cm), the tubes produced by the intermediate sizing mill can be processed by a rotary expansion mill. For example, the intermediate size tube is reheated to a temperature in the range between about 1150 ° C. and about 1250 ° C. by a walking beam furnace and is expanded by an expander mill at a temperature in the range between about 1100 ° C. and about 1200 ° C. It can be expanded to the desired diameter and reheated in-line before final sizing.

  In a non-limiting example, the solid bar is in a tube having an outer diameter in the range between about 6 inches (about 15 cm) to about 16 inches (about 40 cm) and a wall thickness of about 8 mm or more and less than about 35 mm. It can be thermoformed as described above.

  The final microstructure of the formed tube can be determined by the steel composition provided in operation 102 and the heat treatment performed in operation 106. The composition and microstructure can in turn give the properties of the tube to be formed.

  In one embodiment, the enhancement of martensite formation is due to the packet size (the size of the region separated by the high angle boundary that gives higher resistance to crack growth, the higher the deviation, the more the crack crosses the boundary. The high energy required) can be refined and the toughness of the steel pipe for a given yield strength can be improved. Increasing the amount of martensite in the as-quenched tube can further allow the use of higher quenching temperatures for a given strength level. In a further embodiment, higher strength levels can be achieved for a given quenching temperature by replacing bainite in the as-quenched tube with martensite. Accordingly, in one embodiment, it is an object of the present method to achieve a primarily martensitic microstructure at relatively low temperatures (eg, austenite transformation at temperatures below about 450 ° C.). In one embodiment, the martensite microstructure can comprise a volume percent of martensite greater than or equal to about 60%. In further embodiments, the volume percentage of martensite can be about 90% or greater. In further embodiments, the volume percentage of martensite can be about 95% or greater.

  In other embodiments, the hardenability of the steel, i.e. the relative ability of the steel to form martensite when quenched, can be improved by composition and microstructure. In one aspect, the addition of elements such as Cr and Mo is useful in reducing the martensite and bainite transformation temperatures and increases resistance to tempering. Beneficially, a higher tempering temperature can then be used to achieve a given strength level (eg, yield strength). In other aspects, a relatively coarse austenite grain size (eg, about 15 μm to about 100 μm) can improve hardenability.

  In a further aspect, the sulfide stress corrosion cracking (SSC) resistance of steel can be improved by composition and microstructure. In one aspect, SSC can be improved by an increased content of martensite in the tube. In other aspects, tempering at very high temperatures can improve the SSC of the tube, as further detailed below.

In order to promote martensite formation at temperatures below about 450 ° C., the steel composition can further satisfy Equation 1 with the amount of each element given in weight percent:

60C% + Mo% + 1.7Cr%> 10 Equation 1

  When a significant amount of bainite (eg, less than about 40% by volume) is present after quenching, it is retained with substantially high bainite or granular bainite (bainite-like dislocated ferrite and high C martensite). In order to promote relatively fine packets that do not contain a mixture of austenite islands), the temperature at which the bainite forms must be about 540 ° C. or less.

To enhance bainite formation (eg, low bainite) at temperatures below about 540 ° C., the steel composition can further satisfy Equation 2, where the amount of each element is given in weight percent:

60C% + 41Mo% + 34Cr%> 70 Equation 2

  FIG. 2 represents a continuous cooling transformation (CCT) diagram of a steel having a composition within the range shown in Table 1 as indicated by dilatometry. FIG. 2 shows that even with high Cr and Mo contents, the formation of ferrite is substantially avoided, and in order to have a martensite content greater than about 50% by volume, the average prior above about 20 μm. Austenite grain size (AGS) and cooling rates of about 20 ° C./second or more can be used. Furthermore, a cooling rate of about 40 ° C./second or more can be used to provide a microstructure of about 100% martensite.

  Clearly, the typical average cooling rate between about 800 ° C. and 500 ° C. for a tube with a wall thickness between about 8 mm and about 35 mm is lower than about 5 ° C./second, so normalization (eg, austenitization and subsequent resting) Air cooling) cannot achieve the desired martensite microstructure. Water quenching can be used to achieve the desired cooling rate near the center of the wall of the tube and to form martensite and low bainite at temperatures below about 450 ° C. and about 540 ° C., respectively. . Accordingly, the as-rolled tube is reheated in the furnace and is quenched with water in the quenching operation 106A after hot rolling and air cooling.

  For example, in one embodiment of the austenitizing operation 106A, the temperature in the furnace region can be selected to cause the tube to achieve a target austenitizing temperature with a tolerance less than about ± 20 ° C. The target austenitizing temperature can be selected within a range between about 900 ° C and about 1060 ° C. The heating rate can be selected within the range of about 0.1 ° C./second to about 0.3 ° C./second. The soaking period, i.e., the period between the time the tube achieves the final target temperature minus about 10 <0> C and the time it exits the furnace, can be selected within the range of about 300 seconds to about 3600 seconds. The austenitizing temperature and holding time can be selected according to chemical composition, wall thickness and desired austenite grain size. At the exit of the furnace, the tube is scaled and removed immediately to a water quenching system to remove surface oxides.

  In the quenching operation 106B, external and internal cooling can be used to achieve a desired cooling rate (eg, greater than about 20 ° C./second) near the center of the tube wall. As noted above, cooling rates within this range promote the formation of a volume percent of martensite that is greater than about 60%, preferably greater than about 90%, and more preferably greater than about 95%. Can do. The remaining microstructure is low bainite (ie, fine precipitates in bainite laths without coarse precipitates at the lath boundaries, as in the case of high bainite, which is usually formed at temperatures above about 540 ° C). Bainite formed at temperatures below about 540 ° C. with typical morphology including objects.

In one embodiment, the quenching operation 106B with water can be performed by immersing the tube in a tank containing agitated water. The tube can be rapidly rotated during the quenching period to make heat transfer high and uniform and to avoid tube distortion. Furthermore, an internal water jet can be used to remove the vapor generated in the tube. In certain embodiments, the water temperature during the quenching operation 106B can be about 40 ° C. or less, preferably less than about 30 ° C.

  After the quenching operation 106B, the tube can be introduced into another furnace for the tempering operation 106C. In certain embodiments, the tempering temperature should be sufficiently high to produce more carbide with a relatively low dislocation density matrix and a substantially round shape (ie, high degree of spheronization). Can be selected. This spheronization improves the impact toughness of the tube because needle-type carbide at the lath-particle interface can provide an easier crack path.

  Tempering martensite at a sufficiently high temperature to produce a more spherical, dispersed carbide can promote cracks across the particles and better SSC resistance. Crack growth can be slower in steels with multiple hydrogen capture sites, and fine, dispersed precipitates with spheres give better results.

  By forming a microstructure containing tempered martensite as opposed to a bonded microstructure (eg, ferrite-pearlite or ferrite-bainite), the HIC resistance of the steel pipe can be further increased.

  In one embodiment, the tempering temperature can be selected within a range between about 680 ° C. and about 760 ° C. depending on the chemical composition of the steel and the target yield strength. The selected tempering temperature tolerance can be in the range of about ± 15 ° C. The tube can be heated to a selected tempering temperature at a rate between about 0.1 ° C./second and about 0.3 ° C./second. The tube can further be maintained at a selected tempering temperature for a period in the range of about 600 seconds to about 4800 seconds.

  Obviously, the packet size is not significantly affected by the tempering operation 106C. However, the packet size can decrease with decreasing temperature at which austenite transforms. In traditional low carbon steels containing less than about 0.43% carbon equivalents, tempered bainite has a tempered martensite value within the application (eg, less than about 6 μm, for example in the range of about 6 μm to about 2 μm). ), A coarser packet size (for example, 7 to 12 μm) can be indicated.

  The martensite packet size is almost independent of the average austenite particle size, and remains fine (eg, an average particle size of about 6 μm or less) even with a relatively coarse average austenite particle size (eg, 15 μm or 20 μm to about 100 μm). Can be.

  The finishing operation 110 can include, but is not limited to, a strain relief or bending operation. The strain relief operation can be performed at a temperature approximately below the tempering temperature to above approximately 450 ° C.

In one embodiment, the bending operation can be performed by heat induced bending. Thermal induction bending is a thermal deformation process concentrated in a narrow area called hot tape, defined by induction coils (eg, heating rings) and quenching rings that spray water onto the outer surface of the structure to be bent. . A straight (mother) tube is pushed from its back while being secured to an arm constrained so that the front of the tube represents a circular path. Although this constraint induces a bending moment on the entire structure, the tube is plastically deformed substantially only within the hot tape correspondence. Thus, the quench ring serves two simultaneous roles: defining the area under plastic deformation and quenching the thermal bend inline.

  The tube diameter of both the heating ring and the quenching ring is about 20 mm to about 60 mm larger than the outer diameter (OD) of the mother tube. The bending temperature of both the outer and inner surfaces of the tube can be continuously measured with a pyrometer.

  In conventional tube processing, the bend can be subjected to a stress relaxation process that includes heating and holding the bend to a relatively low temperature to achieve final mechanical properties after bending and in-line quenching. However, it will be appreciated that the in-line quenching and stress relaxation operations performed during the finishing operation 110 can produce a different microstructure than that obtained from the offline quenching and tempering operations 106B, 106C. Accordingly, in one aspect of the present disclosure, an offline quenching and tempering process similar to that described above in operations 106B and 106C is performed to substantially regenerate the microstructure obtained after operations 106B and 106C. can do. Thus, the bend is reheated in the furnace, then immediately immersed in a quenching tank containing stirred water and then tempered in the furnace.

  In certain embodiments, the tube can be rotated during quenching in water, and water can flow into the tube using a nozzle, while the bend is fixed and the nozzle is not used during quenching. . Therefore, the quenching effect on the bend may be slightly lower. In further embodiments, the heating rate during the austenitizing and tempering periods can also be slightly different because furnaces with different performance / productivity can be used.

  In one embodiment, tempering after bending and quenching can be performed at a temperature in the range between about 650 ° C and about 760 ° C. The tube can be heated at a rate in the range of about 0.05 ° C./second to about 0.3 ° C./second. A retention time in the range of about 600 seconds to about 3600 seconds can be used after the target tempering temperature is achieved.

  FIG. 3 is an optical micrograph (2% nital etch) depicting the microstructure of an as-quenched tube formed in accordance with the disclosed embodiment. The composition of the tube is 0.10% C, 0.44% Mn, 0.21% Si, 2.0% Cr, 0.93% Mo, 0.14% Ni, 0.05% V, 0.01% Al, 0.006% N, 0.0011% Ca, 0.011% P, 0.003% S, 0.14% Cu. The tube had an outer diameter (OD) of about 273 mm and a wall thickness of about 13.9 mm. As shown in FIG. 3, the as-quenched tube exhibits a microstructure that is primarily martensite and some low bainite. Virtually no ferrite, high bainite or granular bainite is detected. Since austenitization was carried out at about 980 ° C. during a short soak time of about 600 seconds, the average plyer austenite grain size (AGS) of the as-quenched tube measured according to ASTM E112 as a linear intercept was about 20 μm. Met.

  4A and 4B are optical micrographs showing the microstructure of the tube after quenching and tempering according to the disclosed embodiment, whose immersion time is about 2400 seconds. FIG. 4A shows a low magnification (eg, about 200 ×) optical micrograph and FIG. 4B represents the as-quenched tube microstructure after selective etching that can show the boundaries of the prior austenite particles. An optical micrograph at a high magnification (eg, about 1000 ×) is shown. As shown in FIGS. 4A and 4B, the prior austenite grain size is large, about 47 μm, and can further improve the hardenability with a volume percentage of martensite greater than about 90%. Apparently, when the prior austenite grain size after quenching is less than about 20 μm and the volume percentage of martensite exceeds about 60%, the average size of the region separated by high angle grain boundaries (ie, packet size) Is less than approximately 6 μm.

  Even when the prior austenite particles are larger, the primary martensite structure (eg, greater than about 60% by volume martensite) is formed, and low bainite is formed at relatively low temperatures (eg, <540 ° C.). The packet size of the steel after quenching and tempering can be maintained below approximately 6 μm.

  The packet size is based on an image taken by a scanning electron microscope (SEM) using an electron inverse scattering diffraction (EBSD) signal and considering the high angle boundary to have a misorientation greater than about 45 °. It can be measured as an average linear intercept.

  An example of an inverted pole diagram showing the boundary misorientation is shown in FIG. Boundary shifts less than about 3 ° are shown as thin lines, while boundaries showing shifts greater than about 45 ° are shown as bold lines.

  Because the amount of martensite in the microstructure was greater than about 95%, the plier austenite particle size had an average value of about 47 μm, but the linear intercept measurement showed an average packet size value of about 5 μm. The distribution shown in 6 was given.

In addition to coarse precipitates of type M ₃ C, M ₆ C and / or M ₂₃ C ₆ with an average particle size in the range between about 80 nm and about 400 nm on the quench and temper tube, about 40 nm Fine precipitates of the MX, M ₂ X type (where M is Mo or Cr, or V, Nb, Ti if present and X is C or N) with a particle size of less than Moreover, it detected with the transmission electron microscope (TEM).

The total volume percentage of non-metallic inclusions is less than about 0.05%, preferably less than 0.04%. The number of inclusions per square mm of the test area of oxide having a particle size greater than about 15 μm is less than about 0.4 / mm ² .
Only substantially modified round sulfides are present.

  In the following examples, the microstructure and mechanical properties and impact of steel pipes formed using the aforementioned steelmaking process aspects are considered. In particular, for embodiments of the aforementioned composition and heat treatment conditions, austenite grain size, packet size, martensite capacity, low bainite capacity, non-metallic inclusion capacity and inclusions greater than about 15 μm include Checked the parameters. In addition, corresponding mechanical properties including yield and tensile strength, hardness, elongation, toughness and HIC / SSC resistance are also considered.

Mechanical and microstructure properties of quenched and tempered tubes for 80 ksi grade The microstructure and mechanical properties of the steels in Table 2 were studied. In connection with the measurement of microstructure parameters, austenite grain size (AGS) is measured according to ASTM E112, and packet size is an image taken by a scanning electron microscope (SEM) using electron inverse scattering diffraction (EBSD) signals. Using the above average linear intercept, the martensite capacity is measured according to ASTM E562, the low bainite capacity is measured according to ASTM E562, and the volume percentage of non-metallic inclusions uses an optical microscope according to ASTM E1245. The presence of precipitates was measured by automated image analysis and studied by transmission electron microscopy (TEM) using extraction replication.

For mechanical properties, yield strength, tensile strength and elongation are measured according to ASTM E8, hardness is measured according to ASTM E92, impact energy is evaluated on lateral Charpy V-notch specimens according to ISO 148-1. The displacement of the crack tip opening position is measured at about −60 ° C. according to part 1 of BS7488, and the HIC evaluation is performed according to NACE standard TM0284-2003, paragraph 21215 using NACE solution A and a 96 hour test period. It was. SSC evaluation was performed according to NACE TM0177 using test solution A and a test period of about 720 hours at a specified minimum yield stress of about 90%.

  About 90 t of heat having the chemical composition range shown in Table 2 was produced by an arc furnace.

  After tapping, deoxygenation and alloy addition, secondary metallurgical operations were performed in a ladle furnace and trimming station. Next, after calcium treatment and vacuum degassing, the liquid steel was continuously cast on a vertical caster as a round bar of about 330 mm diameter.

  The as-cast bar is reheated to a temperature of about 1300 ° C. with a rotary heat furnace, hot drilled, the hollow is hot rolled with a multi-stand tube rolling mill of a holding mandrel, and according to the method described above in FIG. It was subjected to heat sizing. The manufactured seamless tube had an outer diameter of about 273.2 mm and a wall thickness of about 13.9 mm. The chemical composition measured on the as-rolled seamless tube produced is reported in Table 3.

  Thereafter, the as-rolled tube is austenitized by heating to a temperature of about 920 ° C. for about 2200 seconds in a moving beam furnace, removed by a high-pressure water nozzle, and a tank containing stirring water and an internal water nozzle Tempered with water from the outside and inside. The austenitizing heating rate was about 0.25 ° C./second. The cooling rate used during quenching exceeded about 65 ° C./sec. The quenched tube was quickly transferred to another moving beam furnace for tempering at a temperature of about 710 ° C. over a total time of about 5400 seconds and an immersion time of about 1800 seconds. The tempering heating rate was about 0.2 ° C./second. The cooling used after tempering was performed in still air at a rate of less than about 0.5 ° C./second. All quenched and tempered (Q & T) tubes were dewarped by heat.

  The main parameters representing the microstructure and non-metallic inclusion characteristics of the tube of Example 1 are shown in Table 4.

  The mechanical and corrosion properties of the tube of Example 1 are shown in Tables 5, 6 and 7. Table 5 shows the tensile, elongation, hardness and toughness characteristics of the quenched and tempered tubes. Table 6 shows the two simulated post-weld heat treatments, PWHT1 and PWHT2, and the subsequent yield strength. Post-weld heat treatment 1 (PWHT1) consisted of heating and cooling at a rate of about 80 ° C./hour to a temperature of about 650 ° C. with an immersion time of about 5 hours. Post-weld heat treatment 2 (PWHT2) consisted of heating and cooling at a rate of about 80 ° C./hour to a temperature of about 650 ° C. with a soaking time of about 10 hours. Table 7 shows the measured HIC and SSC resistance of the quenched and tempered tubes.

From the above test results (Table 5, Table 6 and Table 7), it was found that the quenched and tempered tubes were suitable for forming the 80 ksi grade and exhibited the following characteristics:
Yield strength, YS: minimum about 555 MPa (80 ksi) and maximum about 705 MPa (102 ksi),
Ultimate tensile strength, UTS: minimum of about 625 MPa (90 ksi) and maximum of about 825 MPa (120 ksi),
Hardness: less than about 250 HV ₁₀ ,
・ Elongation rate, about 20% or more,
・ YS / UTS ratio, about 0.93 or less,
A minimum impact energy of about 250 J / 200 J (average / individual) at about −70 ° C. for a transverse Charpy V-notch specimen;
• 50% FATT (failure appearance transformation temperature with about 50% shear area) and 80% FATT (about 80% shear area measured in transverse Charpy V-notch specimens tested according to standard ISO 148-1. Excellent toughness with respect to the transformation temperature for the appearance of damage
Excellent vertical crack tip opening deviation (CTOD) at about −60 ° C. (greater than about 0.8 mm),
A minimum of about 555 MPa after simulated post-weld heat treatment [heating and cooling rate of about 80 ° C./hour, immersion temperature of about 650 ° C .; immersion time: 5 hours (PWHT1) and 10 hours (PWHT2)] Yield strength of YS,
HIC (tested according to NACE standard TM0284-2003 clause 21215 using NACE solution A and a test period of about 96 hours) and SSC (test solution A and a specific minimum yield strength of about 90%, SMYS Good resistance to (tested according to NACE TM0177) using about 1 bar of H ₂ S under stress.

Mechanical and microstructure properties of quenched and tempered tubes for 90 ksi grade The microstructure and mechanical properties of the steels in Table 8 were studied as described above for Example 1. Using the chemical composition shown in Table 8, about 90 t of heat-treated product (heat) was produced in an arc furnace.

  After tapping, deoxygenation and alloy addition, secondary metallurgical operations were performed in the ladle furnace and trimming station. Next, after calcium treatment and vacuum degassing, the liquid steel was continuously cast on a vertical caster as a round bar of about 330 mm diameter.

  The as-cast bar is reheated to a temperature of about 1300 ° C. in a rotary furnace, hot drilled, and the hollow is hot-rolled with a multi-stand tube rolling mill of a holding mandrel, according to the method described above in FIG. It was subjected to heat sizing. The manufactured seamless tube had an outer diameter of about 250.8 mm and a wall thickness of 15.2 mm. The chemical composition measured on the as-rolled seamless pipe produced is reported in Table 9.

  The as-rolled tube is then austenitized by heating to a temperature of about 900 ° C. for about 2200 seconds in a moving beam furnace, scaled with a high pressure water nozzle, and a tank containing stirred water and an internal Quenched with water from the outside and inside using a water nozzle. The austenitizing heating rate was about 0.2 ° C./second. The cooling rate used during the quenching period exceeded about 60 ° C./second. The quenched tube was quickly transferred to another moving beam furnace for tempering at a temperature of about 680 ° C. for a total time of about 5400 seconds and an immersion time of about 1800 seconds. The tempering heating rate was about 0.2 ° C./second. The cooling used after tempering was carried out in still air at a rate of less than about 0.5 ° C./second. All quench and temper (Q & T) tubes were subjected to thermal strain relief.

  The main parameters that characterize the microstructure and non-metallic inclusions of the tube of Example 2 are shown in Table 10.

  The mechanical properties of the tube of Example 2 are shown in Table 11. Table 11 shows the tensile, elongation, hardness and toughness characteristics of the quenched and tempered tubes.

From the above test results (Table 11), it was found that the quenched and tempered tubes were suitable for forming the 90 ksi grade and had the following characteristics:
Yield strength, YS: minimum of about 625 MPa (90 ksi) and maximum of about 775 MPa (112 ksi),
Ultimate tensile strength, UTS: minimum of about 695 MPa (100 ksi) and maximum of about 915 MPa (133 ksi),
Hardness: less than about 270 HV ₁₀ ,
・ Elongation rate, about 18% or more,
・ YS / UTS ratio, about 0.95 or less,
A minimum impact energy of about 150 J / about 100 J (average / individual) at about −70 ° C. for a transverse Charpy V-notch specimen;
50% FATT (failure onset transformation temperature with about 50% shear area) and 80% FATT (about 80% shear area) measured in transverse Charpy V-notch specimens tested according to standard ISO 148-1 Excellent toughness with respect to the transformation temperature)
・ ・ Crack length ratio, CLR = 0
・ Crack thickness ratio, CTR% = 0
・ Crack susceptibility ratio, CSR% = 0
Using HIC (NACE solution A and a test period of about 96 hours,
Good resistance to reference TM0284-2003 (tested according to paragraph 21215).

Good SSC resistance was also observed in the specimen. No breakage was observed in the three specimens after about 720 hours. The test was performed according to NACE TM0177 method A using test solution A with a stress value of about 72% or more of the specified minimum yield strength (SMYS) under an H ₂ S pressure of about 1 bar.

Quenched and tempered tube comparative example In this comparative example, an outer diameter of about 324.7 mm and a wall thickness of about 15.7 mm made of a typical line tube steel containing a low carbon equivalent of 0.4%. Using a quenching and tempering tube with a previously described method embodiment, a heat induction bend was made, quenched offline, and tempered.

  The resulting seamless tube was austenitized in a moving beam furnace at about 920 ° C. for about 2200 seconds as described above. The tube was further scaled with a high pressure water nozzle and quenched with water from the outside and inside using a tank containing stirring water and an internal water nozzle. The quenched tube was quickly transferred to another moving beam furnace for tempering at about 660-670 ° C. All quenching and tempering tubes were heat distorted.

  The main parameters that characterize the microstructure and non-metallic inclusions of the Q & T bend are shown in Table 13.

It is recognized that these quenched and tempered tubes do not form enough hardenability to form martensite because they are manufactured using steel with fine austenite particles (about 12 μm). It was. Thus, the microstructure exhibits a major granular bainite microstructure that includes some low bainite and some amount of coarse ferrite (see FIG. 7 and Table 13). Further, the packet size is larger than that of the first and second embodiments.

  Furthermore, these quenched and tempered tubes can achieve a minimum yield strength of about 555 MPa (grade 80 ksi), but due to their different microstructure, higher transformation compared to Examples 1 and 2. It was found to have lower toughness with temperature (Table 14).

Bend microstructure and mechanical properties in quenched and tempered tubes The quenched and tempered tube of Example 1 was used to produce a (5D) bend with a radius about 5 times the outer diameter of the tube.

  The tube was subjected to heat induced bending by heating to a temperature of about 850 ° C. ± 25 ° C. and in-line water quenching. The bend was then reheated in a car furnace to a temperature of about 920 ° C. for a hold of about 15 minutes, transferred to a water bath and immersed in stirred water. The minimum temperature of the bend was higher than about 860 ° C. just before immersion in the water bath, and the water temperature of the water bath was maintained below about 40 ° C.

  After the quenching operation, the as-quenched bend was tempered in an oven set at a temperature in the range between about 700 and about 710 ° C. using a holding time of about 20 minutes.

From the above test results (Table 15, Table 16), it was found that the bends tempered and tempered off-line were suitable for forming the 80 ksi grade and exhibited the following characteristics:
Yield strength, YS: minimum about 555 MPa (80 ksi) and maximum about 705 MPa (102 ksi),
Ultimate tensile strength, UTS: minimum of about 625 MPa (90 ksi) and maximum of about 825 MPa (120 ksi),
-Maximum hardness: less than about 250 HV ₁₀
・ Elongation rate, about 18% or more,
・ YS / UTS ratio, about 0.93 or less,
A minimum impact energy of 250 J / 200 J (average / individual) at about −70 ° C. for transverse Charpy V-notch specimens,
For 50% FATT (transformation temperature at failure occurrence with about 50% shear area) and 80% FATT (transformation temperature for failure appearance with about 80% shear area) measured in transverse Charpy V-notch specimens Excellent toughness,
Excellent longitudinal crack tip opening deviation (CTOD) at about −45 ° C. (greater than about 0.8 mm),
HIC (test according to NACE standard TM0284-2003 clause 21215 using NACE solution A and a test period of about 96 hours) and SSC (test solution A and a specific minimum yield strength of about 90%, stress at SMYS Good resistance to NACE TM0177 using about 1 bar of H ₂ S multiplied by.

Mechanical properties of quenched and tempered tubes for the 70 ksi grade The mechanical properties of the steels in Table 17 were studied as described above for Example 1. An approximately 90 t heat-treated product having the chemical composition range shown in Table 17 was produced by an arc furnace.

  After tapping, deoxygenation and alloy addition, secondary metallurgical operations were performed in a ladle furnace and trimming station. After calcium treatment and vacuum degassing, the liquid steel was continuously cast in a round bar about 330 mm diameter on a vertical caster.

  The as-cast bar is reheated to a temperature of about 1300 ° C. in a rotary heath furnace, hot drilled, and the hollow is hot-rolled by a multi-stand tube mill with a mandrel held, and in FIG. Thermal sizing was performed according to the method described above. The produced seamless tube had an outer diameter of about 273.1 mm and a wall thickness of about 33 mm. The chemical composition measured on the as-rolled seamless tube produced is reported in Table 18.

  The as-rolled tube is then austenitized by heating to a temperature of about 920 ° C. for about 5400 seconds in a moving beam furnace, scaled by a high pressure water nozzle, and a tank containing stirred water and the internal water Quenching with water from the outside and inside using a nozzle. The heating rate for austenitizing was about 0.16 ° C./sec. The cooling rate used during the quenching period was about 25 ° C./second. The quench tube was quickly transferred to another moving beam furnace for tempering treatment at a temperature of about 750 ° C. for a total time of about 8600 seconds and a soaking time of 4200 seconds. The tempering heating rate was about 0.15 ° C./second. The cooling rate used during the tempering period was less than about 0.1 ° C./second. All quenched and tempered (Q & T) tubes were dewarped by heat.

  The mechanical properties and corrosion resistance of the tube of Example 5 are shown in Table 19 and Table 20, respectively. Table 20 shows the properties of tension, elongation, hardness and toughness of the quenched and tempered tubes.

From the above test results (Table 19, Table 20), it was found that the quenched and tempered tubes were suitable for forming the 70 ksi grade and exhibited the following characteristics:
Yield strength, YS: minimum about 70 ksi (485 MPa) and maximum about 92 ksi (63577 MPa (80 ksi),
Ultimate tensile strength, UTS: minimum of about 83 ksi (570 MPa) and maximum of about 110 ksi (760 MPa),
-Maximum hardness: less than about 248 HV ₁₀ ,
・ Elongation rate, about 18% or more,
・ YS / UTS ratio, about 0.93 or less,
A minimum impact energy exceeding about 200 J / about 150 J (average / individual) at about −70 ° C. for a transverse Charpy V-notch specimen;
Excellent for 50% FATT (transformation temperature of failure appearance with about 50% shear area) and 80% FATT (transformation temperature for failure appearance with about 80% shear area) measured in transverse Charpy V-notch specimens Toughness,
HIC (test according to NACE standard TM0284-2003 clause 21215 using NACE solution A and a test period of about 96 hours) and SSC (test solution A and a specific minimum yield strength of about 90%, stress at SMYS Good resistance to (test according to NACE TM0177, using about 1 bar of H ₂ S multiplied by.

  While the above description illustrates, describes and points out basic novel features of the present teachings, various omissions, substitutions and modifications of the details of the illustrated apparatus and their use are intended to It will be understood that it can be practiced by those skilled in the art without departing from the scope. Accordingly, the scope of the present teachings should not be limited to the above discussion, but should be defined by the appended claims.

Claims (33)

0.05 wt% to 0.16 wt% carbon;
0.20% to 0.90% by weight manganese;
0.10 wt% to 0.50 wt% silicon;
1.20% to 2.60% by weight chromium;
0.05 wt% to 0.50 wt% nickel;
0.80% to 1.20% by weight molybdenum;
0.005% to 0.12% by weight of vanadium;
0.008% to 0.04% aluminum by weight;
0.0030 wt% to 0.0120 wt% nitrogen; and 0.0010 wt% to 0.005 wt% calcium;
A steel composition comprising: a seamless steel pipe comprising:
The steel pipe has a wall thickness of 8 mm or more and 35 mm or less, and the steel pipe is processed to have a yield strength of more than 550 MPa (80 ksi), and the microstructure of the steel pipe has a volume percentage martensite of 60% or more and 40% A seamless steel pipe comprising less than% volume percent low bainite. The steel composition further
0-0.80 wt% tungsten;
0-0.030% by weight of niobium;
0-0.020 wt% titanium;
0 to 0.30 weight percent copper;
0 to 0.010% by weight of sulfur;
0-0.020% by weight phosphorus;
0-0.0020% by weight boron;
0-0.020% by weight of arsenic;
0-0.0050% by weight of antimony;
0-0.020 wt% tin;
0 to 0.030% by weight of zirconium;
0-0.030 wt% tantalum;
0-0.0050% by weight of bismuth;
0-0.0030 wt% oxygen;
The remainder of the composition comprising 0-0.00030 wt.% Hydrogen; and iron and impurities:
The steel pipe according to claim 1, comprising: 0.07 wt% to 0.14 wt% carbon of the steel composition;
0.30% to 0.60% by weight manganese;
0.10 wt% to 0.40 wt% silicon;
1.80 wt% to 2.50 wt% chromium;
0.05 wt% to 0.20 wt% nickel;
0.90% to 1.10% by weight molybdenum;
0 to 0.60 wt% tungsten;
0-0.015% by weight of niobium;
0-0.010 wt% titanium;
0.050% to 0.10% by weight of vanadium;
0.010 wt% to 0.030 wt% aluminum;
0.0030 wt% to 0.0100 wt% nitrogen;
0 to 0.20 weight percent copper;
0 to 0.005% by weight of sulfur;
0-0.012% by weight phosphorus;
0.0010% to 0.003% by weight of calcium;
0.0005 wt% to 0.0012 wt% boron;
0 to 0.015% by weight of arsenic;
0-0.0050% by weight of antimony;
0 to 0.015 wt% tin;
0 to 0.015% by weight of zirconium;
0-0.015 wt% tantalum;
0-0.0050% by weight of bismuth;
0-0.0020 wt% oxygen;
The remainder of the composition comprising 0-0.00025 wt.% Hydrogen; and iron and impurities:
The steel pipe according to claim 2, comprising: 0.08 wt% to 0.12 wt% carbon of the steel composition;
0.30 wt% to 0.50 wt% manganese;
0.10 wt% to 0.25 wt% silicon;
2. 10% to 2.40% chromium by weight;
0.05 wt% to 0.20 wt% nickel;
0.95 wt% to 1.10 wt% molybdenum;
0-0.30 wt% tungsten;
0-0.010% by weight of niobium;
0-0.010 wt% titanium;
0.050 wt% to 0.07 wt% vanadium;
0.015 wt% to 0.025 wt% aluminum;
0.0030 wt% to 0.008 wt% nitrogen;
0-0.15 wt% copper;
0-0.003% by weight of sulfur;
0-0.010% by weight phosphorus;
0.0015% to 0.003% by weight of calcium;
0.0008 wt% to 0.0014 wt% boron;
0 to 0.015% by weight of arsenic;
0-0.0050% by weight of antimony;
0 to 0.015 wt% tin;
0-0.010 wt% zirconium;
0-0.010 wt% tantalum;
0-0.0050% by weight of bismuth;
0-0.0015 wt% oxygen;
3. A steel pipe according to claim 2, comprising from 0 to 0.00020% by weight of hydrogen; and the balance of the composition comprising iron and impurities.   The steel pipe of any one of the preceding claims, wherein the yield strength exceeds 625 MPa (90 ksi).   The steel pipe according to any one of the preceding claims, wherein the microstructure of the steel pipe is composed of martensite and low bainite. The steel pipe according to any one of the preceding claims, wherein the microstructure of the steel pipe does not include one or more of ferrite, high bainite and granular bainite.   The steel pipe according to any one of the preceding claims, wherein the volume percentage of martensite is 95% or more and the volume percentage of low bainite is 5% or less.   The steel pipe of claim 8, wherein the volume percentage of martensite is 100%.   The steel pipe according to any one of the preceding claims, wherein the packet size is 6 µm or less. One or more granules with composition MX or M ₂ X having an average particle size of 40 μm or less are present in the steel pipe, wherein M is selected from V, Mo, Nb and Cr, and X is C A steel pipe according to any one of the preceding claims, selected from:   The steel pipe of claim 1, wherein the transformation temperature from ductility to brittleness is lower than -70 ° C. The steel pipe of Claim 1 whose Charpy V-notch energy is 250 J / cm ² or more.   The steel pipe of claim 1, wherein the steel pipe is subjected to a stress of 90% of the yield stress and exhibits at least some failure due to stress corrosion cracking after 720 hours when tested according to NACE TM0177. Providing a carbon steel composition;
The steel composition is formed into a tube having a thickness of 8 mm or more and 35 mm or less, wherein the average austenite grain size in the tube after the formation exceeds 15 μm,
The formed steel pipe is heated to a temperature in the range between 900 ° C. and 1060 ° C. in the first heating operation,
The formed steel pipe is quenched at a rate of 20 ° C./second or more, and the microstructure of the quenched steel pipe is 60% by volume or more martensite and 40% by volume or less low bainite after quenching.
The tempered steel pipe is tempered at a temperature in the range between 680 ° C. and 760 ° C., where the tempered steel pipe has a yield strength of more than 80 ksi and a Charpy V of 100 J / cm ² or more at −70 ° C. -With notch energy, process:
A method of manufacturing a steel pipe, comprising: 0.05% to 0.16% carbon by weight of the steel composition;
0.20% to 0.90% by weight manganese;
0.10 wt% to 0.50 wt% silicon;
1.20% to 2.60% by weight chromium;
0.05 wt% to 0.50 wt% nickel;
0.80% to 1.20% by weight molybdenum;
0.005% to 0.12% by weight of vanadium;
0.008% to 0.04% aluminum by weight;
0.0030 wt% to 0.0120 wt% nitrogen; and 0.0010 wt% to 0.005 wt% calcium:
16. The method of claim 15, comprising: The steel composition further
0-0.80 wt% tungsten;
0-0.030% by weight of niobium;
0-0.020 wt% titanium;
0 to 0.30 weight percent copper;
0 to 0.010% by weight of sulfur;
0-0.020% by weight phosphorus;
0-0.0020% by weight boron;
0-0.020% by weight of arsenic;
0-0.0050% by weight of antimony;
0-0.020 wt% tin;
0 to 0.030% by weight of zirconium;
0-0.030 wt% tantalum;
0-0.0050% by weight of bismuth;
0-0.0030 wt% oxygen;
The process of claim 16 comprising 0-0.00030 wt% hydrogen; and the balance of the composition comprising iron and impurities. 0.07 wt% to 0.14 wt% carbon of the steel composition;
0.30% to 0.60% by weight manganese;
0.10 wt% to 0.40 wt% silicon;
1.80 wt% to 2.50 wt% chromium;
0.05 wt% to 0.20 wt% nickel;
0.90% to 1.10% by weight molybdenum;
0 to 0.60 wt% tungsten;
0-0.015% by weight of niobium;
0-0.010 wt% titanium;
0 to 0.20 weight percent copper;
0 to 0.005% by weight of sulfur;
0-0.012% by weight phosphorus;
0.050% to 0.10% by weight of vanadium;
0.010 wt% to 0.030 wt% aluminum;
0.0030 wt% to 0.0100 wt% nitrogen;
0.0010% to 0.003% by weight of calcium;
0.0005 wt% to 0.0012 wt% boron;
0 to 0.015% by weight of arsenic;
0-0.0050% by weight of antimony;
0 to 0.015 wt% tin;
0 to 0.015% by weight of zirconium;
0-0.015 wt% tantalum;
0-0.0050% by weight of bismuth;
0-0.0020 wt% oxygen;
The remainder of the composition comprising 0-0.00025 wt.% Hydrogen; and iron and impurities:
The method of claim 17 comprising: 0.08 wt% to 0.12 wt% carbon of the steel composition;
0.30 wt% to 0.50 wt% manganese;
0.10 wt% to 0.25 wt% silicon;
2. 10% to 2.40% chromium by weight;
0.05 wt% to 0.20 wt% nickel;
0.95 wt% to 1.10 wt% molybdenum;
0-0.30 wt% tungsten;
0-0.010% by weight of niobium;
0-0.010 wt% titanium;
0.050 wt% to 0.07 wt% vanadium;
0.015 wt% to 0.025 wt% aluminum;
0.0030 wt% to 0.008 wt% nitrogen;
0-0.15 wt% copper;
0-0.003% by weight of sulfur;
0-0.010% by weight phosphorus;
0.0015% to 0.003% by weight of calcium;
0.0008 wt% to 0.0014 wt% boron;
0 to 0.015% by weight of arsenic;
0-0.0050% by weight of antimony;
0 to 0.015 wt% tin;
0-0.010 wt% zirconium; and 0-0.010 wt% tantalum;
0-0.0050% by weight of bismuth;
0-0.0015 wt% oxygen;
The remainder of the composition comprising 0-0.00020% by weight of hydrogen; and iron and impurities:
The method of claim 17 comprising:   20. The method of any of claims 15-19, wherein the yield strength of the steel pipe is greater than 625 MPa (90 ksi) after tempering.   The method according to any one of claims 15 to 19, wherein the microstructure of the steel pipe is composed of martensite and low bainite.   The method according to claim 1, wherein the quenching speed is 40 ° C./second or more, and the microstructure of the steel pipe after quenching is 100% by volume martensite.   The method according to any one of claims 15 to 22, wherein the microstructure of the steel pipe after quenching does not contain one or more of ferrite, high bainite and granular bainite.   The method according to any one of claims 15 to 19, wherein the volume percentage of martensite after quenching is 90% or more, and the volume percentage of low bainite is 10% or less.   The method according to any one of claims 15 to 24, wherein the packet size of the steel pipe after tempering is 6 µm or less. A type having a composition MX or M ₂ X having an average particle size of 40 μm or less after tempering, wherein M is selected from V, Mo, Nb and Cr, and X is selected from C and N The method according to any one of claims 15 to 25, wherein a plurality of granular materials are present in the steel pipe.   The method according to any one of claims 15 to 26, wherein the transformation temperature from ductility to brittleness of the steel pipe after tempering is less than -70 ° C.   The method according to any one of claims 18 to 27, wherein the volume percentage of martensite in the steel pipe is 90% or more, and the volume percentage of low bainite is 10% or less.   The method according to any one of claims 18 to 28, wherein the steel pipe after tempering has a packet size of 6 µm or less. One or more granules having a composition MX or M ₂ X having an average particle size of 40 nm or less, wherein M is selected from V, Mo, Nb and Cr, and X is selected from C and N 30. A method according to any of claims 18 to 29, wherein the article is present in the steel pipe after tempering. 0.10% to 0.13% by weight of carbon;
0.40% to 0.55% manganese by weight;
0.20 wt% to 0.35 wt% silicon;
1.9 wt% to 2.3 wt% chromium;
0.9 wt% to 1.10 wt% molybdenum;
0.001 wt% to 0.005 wt% calcium;
0.050 wt% to 0.07 wt% vanadium;
0.010 wt% to 0.020 wt% aluminum;
The steel pipe has a wall thickness of 8 mm or more and 35 mm or less, and the steel pipe is hot-rolled, then cooled to room temperature, heated to a temperature of 900 ° C. or higher, and quenched at a cooling rate of 40 ° C./second or higher. And tempering at a temperature between 680 ° C. and 760 ° C. to give a prior austenite particle size of 20 to 80 μm, a packet size of 3 μm to 6 μm, and a martensite of 90 volume% or more and a low bainite of 10 volume% or less. And a steel pipe having a yield strength (YS) between 550 MPa (80 ksi) and 705 MPa (102 ksi), an ultimate tensile strength (UTS) between 625 MPa (90 ksi) and 825 MPa (120 ksi), 20% or more Having a YS / UTS ratio of 0.93 or less,
550 MPa (80 ksi) grade seamless steel pipe. 0.10% to 0.13% by weight of carbon;
0.40% to 0.55% manganese by weight;
0.20 wt% to 0.35 wt% silicon;
1.90 wt% to 2.30 wt% chromium;
0.9 wt% to 1.10 wt% molybdenum;
0.001 wt% to 0.005 wt% calcium;
0.050 wt% to 0.07 wt% vanadium and 0.010 wt% to 0.020 wt% aluminum;
Comprising
The steel pipe has a wall thickness of 8 mm or more and 35 mm or less, and the steel pipe is hot-rolled, followed by cooling to room temperature, heating to a temperature of 900 ° C. or higher, quenching at a cooling rate of 20 ° C./second or more, and Processed by tempering at a temperature between 680 ° C. and 760 ° C., finer with 20-60 μm prior austenite particle size, 2 μm-6 μm packet size and 95% by volume martensite and 5% by volume low bainite The structure forms and the steel pipe has a yield strength (YS) between 625 MPa (90 ksi) and 775 MPa (112 ksi), an ultimate tensile strength (UTS) between 695 MPa (100 ksi) and 915 MPa (133 ksi), an extension of more than 18% Having a YS / UTS ratio of 0.95 or less,
625 MPa (90 ksi) grade seamless steel pipe. 0.10% to 0.13% by weight of carbon;
0.40% to 0.55% manganese by weight;
0.20 wt% to 0.35 wt% silicon;
2.00 wt% to 2.450 wt% chromium;
0.9 wt% to 1.10 wt% molybdenum; and 0.001 wt% to 0.005 wt% calcium;
Comprising a steel composition comprising
The steel pipe has a wall thickness of 8 mm or more and 35 mm or less, and the steel pipe is hot-rolled, followed by cooling to room temperature, heating to a temperature of 900 ° C. or higher, quenching at a cooling rate of 20 ° C./second or more, and Processed by tempering at a temperature between 680 ° C. and 760 ° C., a microstructure having an austenite grain size of 20 to 100 μm, a packet size of 4 to 6 μm and a martensite of 60 volume% or more and low bainite of 40 volume% or less. And the steel pipe has a yield strength (YS) between 485 MPa (70 ksi) and 635 MPa (92 ksi), an ultimate tensile strength (UTS) between 570 MPa (83 ksi) and 760 MPa (110 ksi), an elongation of 18% or more and Having a YS / UTS ratio of 0.93 or less,
485 MPa (70 ksi) grade seamless steel pipe.